The ball bearing assemblies used to support the main rotors of high speed gas turbine engines are generally designed to accept both radial and axial loads from the main rotor shaft. Given the extreme operating conditions of such engines, the bearing assemblies must be specifically capable of withstanding high thrust loads while minimizing mass. A turbine engine will produce a large amount of thrust at low altitudes due to the relatively high pressure of the air. As the aircraft climbs in altitude, the thrust produced by the engine will drop due to the relatively low air pressure at higher altitudes. At particularly high altitudes, the radial loads carried by the bearing system may approach the magnitude of the thrust loads. However, this condition is undesirable because it may lead to excursion and skidding of the ball bearings within the bearing system, which may cause excessive wear within the bearing and vibration within the engine.
In addition, high-speed bearings that are supplied excess lubricant may experience an unacceptable rise in temperature due to churning losses. Ideally, a bearing is supplied enough lubricant to support the load-bearing films and carry away the frictional and mechanical heat, but not more. Too much lubricant flow in a high-speed bearing may contribute to the thermal loading of the bearing through viscous losses. Furthermore, where the lubricant is trapped in the bearing, the lubricant is heated by the shearing action of the passing balls, thereby decreasing the effectiveness and useful life of the lubricant.
Accordingly, there is a need for a light weight bearing system capable of carrying thrust loads at high altitude and of recirculating lubrication from within the bearing assembly.